In a conventional disinfection apparatus, in order to perform sterilization and disinfection of tap water or underground water in water and sewerage, deodorization and decoloration of industrial water, bleaching of pulp, sterilization of medical devices, and the like, chemicals such as ozone or chlorine have been used. Incidentally, in the conventional disinfection apparatus, in order to uniformly dissolve ozone and chemicals in treatment water, there has been a need for a stirring device such as a retention tank and a spray pump, it is not possible to immediately cope with changes in water quality and water quantity.
In contrast, according to a disinfection apparatus (an example of an UV-irradiation apparatus) that treats the treatment water as a treatment target using the ultraviolet rays emitted from an ultraviolet ray lamp, it is possible to perform sterilization, disinfection and decoloration of tap water or underground water in the water and sewerage, deodorization and decoloration of industrial water, bleaching of pulp, and the like, and it is also possible to immediately cope with changes in water quality and water quantity by regulating the output of the ultraviolet ray lamp.
However, in the conventional UV-irradiation apparatus, in order to monitor whether ultraviolet rays with ultraviolet ray intensity required for treatment of the treatment water are emitted from the ultraviolet ray lamp, the ultraviolet ray permeability of the treatment water is measured by a dedicated measuring device, and it is determined whether the ultraviolet ray intensity emitted from the ultraviolet ray lamp satisfies a prescribed value defined by the operation specification of the UV-irradiation apparatus, based on the measurement result.